1. Field of the Invention
The present invention relates to a method for manufacturing semiconductor devices and, more specifically to, a method for manufacturing complementary MISFETs having a gate insulating film made of a high-dielectric constant material.
2. Related Art
In recent years, in a semiconductor device including metal-insulator-semiconductor field effect transistors (MISFETs), the film thickness of gate insulating films has been becoming thinner as gate length has become shorter. This trend increases a leakage current due to the quantum tunneling effect, thus suppressing dissipation power of the MISFET from being lowered.
Conventionally, as the gate insulating film, a silicon oxide film (SiO2) and a silicon oxy-nitride film (SiON) have been used. However, by using these materials, the gate insulating film cannot easily be thinned further while suppressing the leakage current. The thinning of the gate insulating film is now up against a physical limit.
To satisfy both of suppression of the leakage current and thinning of the effective gate insulating film thickness (also referred to as effective oxide film thickness, film thickness calculated as SiO2, or equivalent oxide thickness (EOT)), a so-called high-dielectric constant gate insulating film technology is proposed which uses gate insulating films made of a high-dielectric constant material (hereinafter referred to as high-k material) (see, for example, Japanese Patent Application Laid-Open No. 2008-72001). As the high-k materials, hafnium-based oxides have been discussed such as hafnium oxide (HfO2) and nitrided hafnium silicate (HfSiON).
However, in the case of forming a high-k material as the gate insulating film on a silicon substrate, it is impossible to avoid a low-dielectric constant layer (interface transition layer) mainly made of silicon oxide occurring on the interface between the gate insulating film and the silicon boundary. Therefore, it is difficult to form a gate insulating film having an extremely small effective oxide film thickness.
To solve this problem, a method is proposed for realizing an extremely small effective film thickness of the gate insulating film necessary in the next generation semiconductor devices (see, for example, Toshiba Corporation Review Vol. 62, No. 2 (2007), pp. 37-41). By this method, a film made of a high-k material (hereinafter referred to as high-k film) is directly junctioned to the surface of a silicon substrate. Other methods may be available for forming a high-k film (HfO2) having an extremely thin HfSiOx interface layer between itself and a silicon substrate on the silicon substrate. Those methods will prevent formation of the aforesaid interface transition layer mainly made of a silicon oxide film.